1. Field of the Invention
The present invention relates to an ink-jet recording process for recording information such as images, letters and symbols on paper, light-transmissive recording medium or the like using an ink-jet recording apparatus.
2. Related Background Art
Ink-jet recording is known as a superior recording method which is not particularly demanding in choice of recording mediums, and so research and development have been extensively made on recording apparatus, recording processes and recording mediums.
However, in the ink-jet recording apparatus developed and made commercially available, it has actually been impossible to simultaneously obtain;
(i) a recorded image having a high optical density (OD); PA0 (ii) a recorded image which is good in print quality and free from any feathering on the peripheral part of letters or images; and PA0 (iii) a good drying time characteristic; PA0 (i) which are not particular in choice of recording faces (or are not particular in choice of materials such as paper or films and of the reverse side or obverse side thereof); PA0 (ii) which have a high optical density; PA0 (iii) which are good in print quality and free from feathering; and PA0 (iv) which have a good drying time characteristic; and there have been developed (1) a process in which recording is carried out using a strongly alkaline ink of about pH 13 (Japanese Laid-Open Patent Application No. 102970/1982) and (2) a process in which recording is carried out using an ink-jet recording apparatus of a continuous type such as a charge-controlled type, etc. PA0 (i) which is not especially particular in choice of recording faces (or is not particular in choice of materials such as paper or films and of the reverse side or obverse side thereof); PA0 (ii) which achieves a high optical density; PA0 (iii) which is good in print quality and free from feathering; and PA0 (iv) which achieves a good drying time characteristic;
unless there are used recording mediums developed for exclusive use in an ink-jet recording which are called ink-jet recording paper or ink-jet recording transparenty films.
The above performances (i) to (iii) can not be simultaneously satisfied when recording is carried out on recording media such as paper including electrophotographic recording paper (PPC paper), letter paper, bond paper, post cards, writing paper, envelopes, report paper, etc. generally used in offices, homes, etc. and transparent films (OHP films) with use of conventionally known ink-jet recording apparatus. Even when an ink-jet recording paper is used, there has also been accompanied with the disadvantage such that recording can not be performed on both sides thereof since most ink-jet recording paper is only a one-side coated paper, and thus the grade of prints and the drying time characteristic may be lowered if recording is carried out on the side on which no coating was applied. Thus, various developments have been made for the purpose of obtaining recorded images;
However, it is known in the process of (1) that an ink so strongly alkaline can be dangerous to handle, that although good printing can be performed on acidic sized paper employing rosin or the like, there are posed the disadvantages such that both drying time characteristic and quality of prints may be greatly lowered when there is used neutral paper employing an alkyl ketone dimer or the like, and also that strike-through tends to occur probably because of large permeability of the ink into the paper.
In the process of the above (2), although it is a process that can achieve a recording of a relatively high density, there are limitations in the precision of the nozzles from which an ink is ejected, and thus fine ink droplets can be stably ejected only with difficulty. As a result, unless the recording density is controlled to substantially no more than about 9.5 dots/mm (240 dots/inch), the drying time characteristic may be lowered (i.e., the recording surface may be soiled when smeared with fingers) and the irregular spreading of dots (feathering) may occur, because of an overly large amount of the ink to be fixed on the recording face, so that there is obtained a low print quality, i.e., a recorded image having blurred peripheral parts.
With the recording density of about 9.5 dots/mm, there have been accompanied with the disadvantages such that it is impossible to carry out sharp printing for close (or tight) chinese characters (such as " ") or sometimes difficult to carry out the recording that can be smooth and natural in oblique line part or curved line part such as "/", " " or "O", and every dot can be visually observed, giving recorded images of conspicuous ruggedness and lower grade.
The prior art includes the following documents relating to the below-listed ink-jet recording conditions:
1. Amount of ink adherence per unit area.
Itoh et al., "High Optical Density Recording Paper for Ink-Jet Printing," National Technical Report, Vol. 28, No. 6, Dec. 1982, discusses ejecting different amounts of ink and evaluating recording quality, as pointed out in Table 2 (which discloses ejecting up to 9.4 pl/cm.sup.2 of ink) and FIG. 2b (which shows a pattern printed at 2 lines/mm);
U.S. Pat. No. 4,503,111 discusses recording with ink coverage at 1.5 .mu.l/cm.sup.2 (column 5, lines 1-3; see also column 6, lines 61-63); and
Japanese Laid-Open Patent Application No. 60-172582 discloses that the maximum amount of ink applied to recording paper is 3.5 mg/cm.sup.2, which, if the specific gravity of the ink is assumed to be 1.0, is 3.5.times.10.sup.6 pl/cm.sup.2.
2. Concentration of colorants in inks.
U.S. Pat. No. 4,381,946 discloses dye concentration in inks of 0.5% to 8% by weight (column 4, line 8-18); and
U.S. Pat. No. 4,295,889 discloses dye concentrations in inks of 0.1% to 20% by weight (column 4, lines 44-48).
3. Paper basis weight.
U.S. Pat. No. 4,440,827 discloses recording paper with a basis weight of 70 to 83 g/m.sup.2 (columns 6 and 8, Tables 1 and 9);
U.S. Pat. No. 4,478,910 describes recording paper with a basis weight of 60 to 85 g/m.sup.2 (columns 4-6, Tables 1 and 2); and
European Patent Application 174,859 discloses recording paper with a basis weight of 50 to 90 g/m.sup.2 having an ink acceptor layer.
4. Ink solvent boiling point.
U.S. Pat. No. 4,295,889 (see No. 2 above) discloses the following solvents for inks, which have the following boiling points:
______________________________________ Solvent Boiling Point (.degree.C.) ______________________________________ Methyl alcohol 64.5 Ethyl alcohol 78 n-Propyl alcohol 97 iso-Propyl alcohol 82.7 n-Butyl alcohol 118 sec-Butyl alcohol 98.5 tert-Butyl alcohol 82.5 iso-Butyl alcohol 108 Dimethylformamide 153 Dimethylacetamide 165 Acetone 56.5 Diacetone alcohol 167.9 Tetrahydrofuran 64-65 Dioxane 101 Polyethylene glycol &gt;300 Polypropylene glycol &gt;300 Ethylene glycol 197 Propylene glycol 188.2 Butylene glycol 190.5 Triethylene glycol 179 Thiodiglycol 282 Hexylene glycol 197 Diethylene glycol 245 Glycerol 290 Ethylene glycol methyl ether 124.5 Diethylene glycol methyl ether 194.2 Diethylene glycol ethyl ether 195 Triethylene glycol monomethyl ether 249 N-Methyl-2-pyrrolidone 202 1,3-Dimethyl-2-imidazolinone 226. ______________________________________